Intervertebral spacer

ABSTRACT

Disclosed is an assembly and method for implant installation between adjacent vertebral bodies of a patient. The implant has a support body and a rotatable insert therein and the support body is curved for installation between adjacent vertebral bodies transforaminally. An installation instrument is also disclosed for removable attachment to implant and engagement with the rotatable insert to selectively permit rotation between the insert and the support body. The installation instrument extends along a longitudinal tool axis and when the installation instrument is in a first position the insert is rotationally fixed with respect to the support body and when the installation instrument is in a second position the support body may rotate with respect to the insert.

CROSS REFERENCE TO RELATED APPLICATIONS

This patent application is a continuation of U.S. patent applicationSer. No. 16/159,926, filed on Oct. 15, 2018, which is a continuation ofU.S. patent application Ser. No. 15/695,593, filed on Sep. 5, 2017(published as U.S. Patent Publication No. 2017/0360574), which is acontinuation of U.S. patent application Ser. No. 14/683,502, filed Apr.10, 2015, now issued as U.S. Pat. No. 9,782,269, which is a continuationof U.S. patent application Ser. No. 13/406,663, filed Feb. 28, 2012, nowissued as U.S. Pat. No. 9,138,330, which is a continuation of U.S.patent application Ser. No. 12/250,168 filed on Oct. 13, 2008, nowissued as U.S. Pat. No. 8,147,554. Each of these references is herebyincorporated by reference herein in its entirety.

FIELD OF THE INVENTION

The present invention generally relates to intervertebral spacers forfusing vertebral bodies. In particular, certain embodiments are directedto an intervertebral spacer configured and dimensioned to be implantedtransforaminally.

BACKGROUND OF THE INVENTION

The vertebrate spine is the axis of the skeleton providing structuralsupport for the other body parts. In humans, the normal spine has sevencervical, twelve thoracic and five lumbar segments. The lumbar spinesits upon the sacrum, which then attaches to the pelvis, and in turn issupported by the hip and leg bones. The bony vertebral bodies of thespine are separated by intervertebral discs, which act as joints butallow known degrees of flexion, extension, lateral bending, and axialrotation.

The typical vertebra has a thick anterior bone mass called the vertebralbody, with a neural (vertebral) arch that arises from the posteriorsurface of the vertebral body. The centra of adjacent vertebrae aresupported by intervertebral discs. Each neural arch combines with theposterior surface of the vertebral body and encloses a vertebralforamen. The vertebral foramina of adjacent vertebrae are aligned toform a vertebral canal, through which the spinal sac, cord and nerverootlets pass. The portion of the neural arch which extends posteriorlyand acts to protect the spinal cord's posterior side is known as thelamina. Projecting from the posterior region of the neural arch is thespinous process.

The intervertebral disc primarily serves as a mechanical cushionpermitting controlled motion between vertebral segments of the axialskeleton. The normal disc is a unique, mixed structure, comprised ofthree component tissues: the nucleus pulpous (“nucleus”), the annulusfibrosus (“annulus”) and two vertebral end plates. The two vertebral endplates are composed of thin cartilage overlying a thin layer of hard,cortical bone which attaches to the spongy, richly vascular, cancellousbone of the vertebral body. The end plates thus act to attach adjacentvertebrae to the disc. In other words, a transitional zone is created bythe end plates between the malleable disc and the bony vertebrae.

The spinal disc and/or vertebral bodies may be displaced or damaged dueto trauma, disease, degenerative defects, or wear over an extendedperiod of time. One result of this displacement or damage to a spinaldisc or vertebral body may be chronic back pain.

A disc herniation occurs when the annulus fibers are weakened or tornand the inner tissue of the nucleus becomes permanently bulged,distended, or extruded out of its normal, internal annulus confines. Themass of a herniated or “slipped” nucleus tissue can compress a spinalnerve, resulting in leg pain, loss of muscle control, or even paralysis.Alternatively, with discal degeneration, the nucleus loses its waterbinding ability and deflates, as though the air had been let out of atire. Subsequently, the height of the nucleus decreases causing theannulus to buckle in areas where the laminated plies are loosely bonded.As these overlapping laminated plies of the annulus begin to buckle andseparate, either circumferential or radial annular tears may occur,which may contribute to persistent or disabling back pain. Adjacent,ancillary spinal facet joints will also be forced into an overridingposition, which may create additional back pain.

Whenever the nucleus tissue is herniated or removed by surgery, the discspace will narrow and may lose much of its normal stability. In manycases, to alleviate back pain from degenerated or herniated discs, thedisc is removed along with all or part of at least one neighboringvertebrae and is replaced by an implant that promotes fusion of theremaining bony anatomy.

While this treatment may help alleviate the pain once the vertebrae havebeen successfully fused together, there remains the possibility that thesurgical procedure may not successfully or fully bring about theintended fusion. The success or failure of spinal fusion may depend uponseveral factors. For instance, the spacer—or implant or cage—used tofill the space left by the removed disc and bony anatomy must besufficiently strong to support the spine under a wide range of loadingconditions. The spacer should also be configured so that it is likely toremain in place once it has been positioned in the spine by the surgeon.Additionally, the material used for the spacer should be a biocompatiblematerial and should have a configuration that promotes bony ingrowth.

As a result, the design of the implant should provide sufficientrigidity and strength to resist deformation when loading forces areapplied to it. Likewise, the implant should sufficiently resist slidingor movement of the implant as a result of torsional or shearing loads.Often, these parameters lead designers to select predominantly solidstructures made of bone or of radio opaque materials such as titanium.

Instrumentation and specialized tools for insertion of an intervertebralimplant is yet another design parameter to consider when designing aspacer. Spinal fusion procedures can present several challenges becauseof the small clearances around the spacer when it is being inserted intoposition. For instance, the instrumentation used may securely grip theimplant on opposing sides or surfaces. For example, the superior andinferior surfaces may have one or more regions in which no grippingteeth are present. Such protrusion-free zones enable the implant to begrasped and manipulated by elongate rectangular blades. Notably, theseprotrusion-free zones are not formed as channels cut into the surface ofthe implant in order to maintain the strength and integrity of theimplant so that it is less prone to failure. Thus, the clearancerequired in order to insert the spacer must be higher than the spaceritself in order to accommodate the instrumentation. For this reason,distraction of the treated area typically is greater than the implantitself.

Similarly, when the gripping tools used to manipulate and insert theimplant are on the sides of the spacer, additional clearance typicallyis needed in order to accommodate the added width of the insertion toolblades. Such increases in height or width of the profile of the spacerwhen coupled or in communication with instrumentation means thatadditional space is needed in order to insert the spacer. In somecircumstances, providing for this additional clearance space can bedifficult to achieve.

Thus, despite known devices that promote fusion of a treated area of thespine, there remains a need for spacer designs that optimize bonyingrowth, have structural rigidity to support the spine under a varietyof loading conditions, and allow for insertion through a smallerprofile.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective exploded view of one embodiment of an implantaccording to the invention;

FIG. 2 is a top view of an assembled implant of the embodiment of FIG.1;

FIG. 3 is a cross-sectional view of the implant of FIG. 2 taken alongthe line A-A:

FIGS. 4A-4D are perspective views of a support body of the implant ofFIGS. 1-3

FIGS. 5A-5D are top, rear, side, and front views, respectively, of thesupport body FIGS. 1-4;

FIG. 6 is an exploded view of one embodiment of an insertion instrumentaccording to the invention;

FIG. 7 is an assembled view of the instrument of FIG. 6 having animplant of FIG. 1 attached thereto;

FIG. 8 is an assembled view of an alternate embodiment of an instrumentaccording to the invention;

FIGS. 9-12 are views depicting the articulation of the implant of FIG. 1with respect to installation instruments according to the invention;

FIGS. 13-16 are views showing the placement of an implant of theinvention between vertebral bodies using an instrument of the invention;and

FIGS. 17-18 are side perspective views of alternative embodiments ofimplants.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

Embodiments of the present invention are generally directed toimplantable spacers that can be used to fuse together a treated area ofthe spine while restoring or maintaining the proper spacing and naturalcurvature of the spine. The treated area may include regions betweenadjacent vertebral bodies so that the height of the spacer correspondsapproximately to the height of the disc. In some embodiments, the heightof the spacer of may be greater than the height of a disc alone. Forinstance, the treated area of the spine may be prepared by the physicianby removing all or part of at least one vertebral body.

As explained in greater detail below, several features of the inventionallow for more efficient insertion or placement of the spacers into adesired position. Additionally, aspects of the invention also providesuitable rigidity and integrity for supporting the spine during fusionwhile also providing greater ability to confirm that fusion is takingplace as desired.

One feature that may result in more efficient insertion or placement ofembodiments of spacers according to the invention concerns how thespacers may receive instrumentation for manipulation and insertion ofthe spacer into its proper position. As mentioned above, conventionaltooling for manipulating the spacer generally requires that there begreater clearances in the treated area than needed for the spacer alonein order to accommodate the portions of the tooling that extend beyondthe surface of the spacer. In contrast, some embodiments of the presentinvention do not require an insertion area that is larger than thespacer. Thus, in one embodiment the spacer has one or more toolingengagement surfaces disposed on opposing surfaces of the spacer. Thespacer is thereby capable of being manipulated or inserted into positionby gripping the engagement surfaces with a suitable tool.

For instance, one example of a suitable gripping tool may be a devicehaving a plurality of arms that may be selectively expanded or openedand subsequently closed or compressed onto the engagement surface. Inone embodiment, the engagement surface is formed from plurality ofchannels formed in the spacer. In one variation, there is a channellocated at each engagement surface in which the arms of the manipulatingor insertion tool may be disposed to further help ensure that thetooling does not project beyond the largest cross-sectional view of thespacer when viewed along the direction in which the spacer will travelduring insertion.

Once the spacer has been moved into position, it is desirable for it tohave sufficient structural rigidity or integrity that the spacer doesnot buckle or otherwise fail under loading by the spine. In general, thespacer should be configured so that it meets requirements for axialcompression, axial torsion, subsidence, and resistance to expulsion. Asused herein, structural rigidity or integrity refers to the capabilityof the spacer to resist axial compression and axial torsion withoutbuckling or otherwise failing.

In order to minimize the risk of failure from compressive or torsionalloading, it is preferred that the spacer meets or exceeds minimumstructural rigidity values. In general, it is preferred that therigidity of the spacer exceeds the rigidity of the neighboring vertebralbodies to ensure that the spacer does not collapse or fail under loadingconditions first. For instance, in one embodiment the spacer is capableof bearing axial compression loads of about 10 kN or more, while inanother the spacer is capable of undergoing axial compression loading ofabout 15 kN or more. In general, increases in rigidity often can lead tolarger bulk or size of the spacer. Thus, while the spacer should besufficiently rigid to withstand expected loading conditions, eventuallythe benefits of increasing rigidity become outweighed by otherdisadvantages such as overall size of the spacer or its ability toprovide through holes for promoting fusion. For example, in oneembodiment, the spacer 30 is capable of bearing axial loads of about 30kN or less, while in another the spacer is capable of withstanding about25 kN or less of axial compression. Additionally, these upper and lowerlimits may be combined in any manner desired. For instance, a spacer ofthe present invention may be capable of bearing axial compression loadsfrom about 10 kN to about 30 kN, from about 15 kN to about 25 kN, orfrom about 10 kN to about 25 kN.

Likewise, the spacer may be capable of resisting torsional loading atleast to the degree of torsional resistance that a healthy disc couldprovide. In one embodiment, the spacer is capable of resisting about 1.8Nm or more of torsional loading. In alternate embodiments, however, thespacer is capable of resisting about 40 Nm or more of torsional loading.

In addition to having structural rigidity or integrity, the spacershould be configured so that it subsides in a desired position withoutsubstantially sinking into or piercing nearby anatomy when subjected toaxial loading. Different regions of the spine have different sizedvertebral bodies, each of which may be subjected to different types andamounts of loading. For instance, vertebral bodies in the lumbar regionof the spine are generally larger than vertebral bodies in the cervicalregion. Typically, the lumbar region of the spine may be subjected toapproximately 450 N or more of standing trunk weight, whereas thecervical region may only be subjected to about 50 N of head weight. Thelarger size of the vertebral bodies in the lumbar region helpsdistribute the increased loading over a greater area.

The spacer also may be configured to resist threshold amounts ofexpulsion forces. For example, a normal disc may be capable of resistingshear stresses up to about 150 N. Therefore, the spacer may beconfigured to withstand at least the same degree of shear loadingwithout moving out of its desired position. More preferably, however,the spacer is capable of withstanding even greater shear stresses. Forexample, the disc may be capable of withstanding about 600 N or more ofshear loading, and in another embodiment it is capable of withstandingabout 900 N or more. This feature of the spacer is primarily dependenton the configuration of the protrusions placed on the upper and lowersurfaces of the spacer. Thus, the spacer may be configured to withstandeven more shear stress, such as loading of about 1000 N or more.

The height of a spacer may be varied depending upon the height of thearea of the spine that is to be treated. For this reason, a plurality ofspacers having varying heights may be provided to a physician. Thisallows the physician to select from a variety of spacer heights during asurgical procedure. In one embodiment, the height of the window alsoincreases as the overall height of each spacer increases, which in turnmay change or alter the relationship between the area of the window andthe area of the blocked by the material forming the spacer. Onealternative way to describe the spacer window size is by the span orhorizontal width of the window.

Fusion typically is expected to begin in the anterior region of thetreated area. One reason for this may be that the anterior region mayundergo more axial loading than the posterior region. The additionalpressure in this region may trigger fusion to begin. Thus, the lines ofsight created by the openings or windows may be positioned so that theyintersect in an anterior region of the treated area.

Any biocompatible material may be used to form a spacer of the presentinvention. For example, suitable materials for forming spacers of thepresent invention may be include, but are not limited to, titanium andother surgical grade metals and metal alloys. Since metals and metalalloys generally are radio-opaque, several of the advantages ofproviding large openings or windows in order to view the treated areawill be apparent when the spacer is made of these materials. Inaddition, radiolucent materials also may be used to form spacers of thepresent invention. For example, either all or a substantial portion ofthe spacer may be formed of Polyetheretherketone (PEEK) polymers orsimilar materials. A spacer made of PEEK or other radiolucent materialmay further comprise a pin disposed within the spacer that helps aphysician identify the orientation of the spacer during insertion. Othermaterials likewise may be used to from all or part of the spacers of thepresent invention. For example, all or a portion of the spacer may beformed of bioresorbable materials that, over time, may be resorbed andreplaced by bone.

These and other features are explained more fully in the embodimentsillustrated below. It should be understood that in general the featuresof one embodiment also may be used in combination with features ofanother embodiment and that the embodiments are not intended to limitthe scope of the invention.

Referring to FIGS. 1-5, one embodiment of a spacer or implant 10according to the invention comprises a support body 12 and a rotatableinsert 14 assembly. Support body 12 may have an arcuate or curved shapeextending laterally from a proximal end portion 16 to a distal endportion 18. The distal end 18 portion may have a tapered end 20narrowing towards the distal most end. In one embodiment, a longitudinalopening 22 may extend through implant 10 to facilitate bone growththrough implant 10 and fusion when implanted. A plurality of protrusionsor teeth 24 may be provided along the superior and inferior end surfacesto facilitate prevention of expulsion of implant 10 from between theadjacent vertebral bodies between which it may be implanted.

In one variation a longitudinal hole 26 may be provided to accommodateinsert 14. In this regard, hole 26 may be configured and dimensioned toreceive insert 14 and permit rotational movement between insert 14 andsupport body 12. In one variation, insert 14 has a cylindrical shape andallows the implant 10 to turn freely when desired but may be locked,fixed, or stabilized in a predetermined position by insertion tool 28.For example, the position may be locked for initial insertion by asleeve, holder, or stabilization member. According to one embodiment,insert 14 may be captured within hole 26 of support body 12 by acircumferential rib 32 on the insert 14 that mates to a correspondingindentation shaped on the support body 12. In this regard, onceassembled, insert 14 is generally constrained longitudinally withrespect to support body 12. Insert 14 may have a threaded hole 34therein extending transverse to longitudinal axis 36 to interface withinsertion tool 28. An indention, marking or other alignment mechanism 37may be aligned with hole 34 and may be provided in the superior surfaceof insert 14 so that a user may visually align the hole 34 with anopening in the proximal end 16 of implant 10. A slot 38 may be providedadjacent the threaded hole 34 to provide counter-torque and orstabilization to insert 14 and to facilitate threaded insertion of theinsertion instrument 28 with the insert 14. In one variation, slot 38runs generally perpendicular to threaded hole 34. As shown in FIGS. 1,4A-D, and 5B, the proximal end portion 16 of implant 10 may have arounded shape and may include one or more slots or grooves 40, 46 toengage insertion instrument 28 to facilitate insertion of spacer 10. Inone embodiment, groove 40 extends adjacent the proximal end and extendsalong the interior curved wall of support body 12. Groove 40 has anopening in communication with hole 26 to allow a part of insertion tool28 to engage threaded hole 34. For example, in one variation insertiontool 28 may include a shaft 42 with a threaded tip portion 44 tothreadedly engage insert 14. As shown in FIG. 4B another slot 46 may beprovided adjacent the outer curved wall of support body 12. One or moreindentations 48 may be provided within groove 46 to accommodateprotrusions on insertion tool to enhance gripping of the insertion tool28 with spacer 10.

One or more openings 50 may be provided extending through the curvedside walls and into the central longitudinal opening 22. Openings 50 mayfacilitate bony ingrowth and may provide a window through which bonyfusion may be visually confirmed. As best seen in FIGS. 2-3, whenimplant 10 is made from radiolucent material such as PEEK, one or moreradio-opaque markers 51 may be integrated into implant 10 such that theimplant may be viewed and or located when using fluoroscopy.

Referring to FIG. 6, an exploded view of one embodiment of an insertioninstrument 28 according to the invention is shown. Instrument 28generally comprises an implant stabilizer 62, an insert stabilizer 64,and a central shaft 42 extending through the implant and insertstabilizers 62, 64. As explained above, central shaft 42 has a threadeddistal tip portion 44 to threadedly engage insert 14. Insert stabilizer64 may have a generally cylindrical body extending from a proximal end66 to a distal end 68. Insert stabilizer 64 is cannulated to accommodatecentral shaft 42 therethrough. In one variation, distal end 68 of insertstabilizer 64 has a forked free end 70 with a pair of tongs or prongs 72spaced apart and extending distally therefrom. The prongs 72 areconfigured and dimensioned to engage slot 38 of insert 14. A keyed slot74 may be provided adjacent the distal end 68 and extending proximallytherefrom. Keyed slot 74 is generally configured and dimensioned toengage and interface with a pin 76 provided in implant stabilizer 62.The proximal end 66 of insert stabilizer 64 may have an opening 78extending transversely therethrough configured and dimensioned toreceive a rotatable wheel or thumbwheel 80. Thumbwheel 80 has a centralopening configured to receive central shaft 42 therethrough and a setscrew 82 may extend through the thumbwheel 80 to axially androtationally fix central shaft 42 to thumbwheel 80 so as to rotationallyconstrain central shaft 42 to thumbwheel 80. In this regard, inoperation a surgeon utilizing the installation instrument 28 may rotatethe central shaft 42 by rotating the thumbwheel 80 about axis 84. Anexternally threaded region 86 may be provided adjacent opening 78 tointerface or otherwise engage an internally threaded stabilizer lockwheel 88.

Implant stabilizer 62 may be a generally cylindrical cannulated bodyextending from a proximal end 92 to a distal end 94 configured anddimensioned to extend over insert stabilizer 64. In one variation,distal end 94 of implant stabilizer 62 has a forked free end 96 with apair of tongs or prongs 98 spaced apart and extending distallytherefrom. Prongs 98 are configured and dimensioned to engage the slotsor grooves 40, 46 of implant 12. A flange or shoulder 100 may beprovided adjacent proximal end 92 and flange 100 may engage a slot 102in stabilizer lock wheel 88 to constrain axial movement between theimplant stabilizer 62 and stabilizer lock wheel 88 yet allow rotationalmovement therebetween. In this regard, as stabilizer lock wheel 88 isrotated about threaded region 86, the distal end 94 of implantstabilizer 62 may be advanced or moved along axis 84 to engage the slots40, 46 on implant 10 so as to stabilize implant 10 with respect toprongs 98. With prongs 98 engaged with slots 40, 46, implant 10 isrigidly attached to instrument 28 and locked rotationally such thatimplant 10 is prevented from being rotated or articulated with respectto insertion tool axis 84. Those skilled in the art may appreciate thedesirability of such a feature when, for example, the spacer may behammered or impacted into place between adjacent vertebrae. In thisregard, the surgeon user may apply axial force on the insertion toolaxis without risk that such impaction will cause the spacer to rotate orarticulate with respect to axis 84. If and when the surgeon user desiresto allow the implant to articulate with respect to axis 84, he maydisengage the implant stabilizer 62 from the implant to selectivelyallow the implant to articulate with respect to axis 84. In onevariation, an ergonomic handle 104 may be connected to the proximal end92 of instrument 28 to facilitate handling and/or impaction. Referringto FIG. 8, in an alternate embodiment an alternate T-shaped handle 106may be connected to proximal end 92 of instrument 28. Those skilled inthe art may appreciate that such a T-shaped handle may facilitate, amongother things, enhanced visibility of the surgical site by a surgeonuser.

Referring now to FIGS. 9-12, the articulatability of implant 10 withrespect to installation instrument 28 is shown. As shown in FIG. 9,implant stabilizer 62 is engaged on implant 10 so as to stabilizeimplant 10 and/or rigidly attach to instrument 28. In this position,implant 10 is locked rotationally such that it is prevented from beingrotated or articulated with respect to insertion tool axis 84. In onevariation, shown in FIG. 9, implant 10 may extend in a generally axialdirection along axis 84 from the end of tool 28. Referring to FIGS.10-12, with implant stabilizer 62 disengaged from implant 10, theimplant is free to rotate or articulate with respect to axis 84 ofinsertion tool 28. In one variation, implant 10 may articulate or rotatebetween about 0 degrees (FIG. 10) and about 90 degrees (FIG. 12).

Referring now to FIGS. 13-16, one embodiment of a method of usingimplant 10 in conjunction with inserter 28 is shown. In a first step,the implant 10 may be threadedly engaged onto insertion tool 28 usingthumbwheel 80 to rotate central shaft 42 and threadedly engage thethreaded distal tip portion 44 into threaded hole 34 of insert 14. Thestabilizer lock 88 may then be turned clockwise to engage implantstabilizer prongs 98 with slots 40, 46 on implant 10 to prevent implant10 from rotating about insertion tool axis 84. In this position, withthe implant 10 fixed or stabilized with respect to the insertioninstrument 28, the insertion tool 28 may be impacted from the proximalend. For instance according to one method shown in FIG. 13, a surgeonmay impact the proximal end of handle 104 to achieve a desiredpositioning or depth between adjacent vertebral bodies using, forexample, a transforaminal approach. As explained above, the surgeon usermay apply axial force on the insertion tool axis without risk that suchimpaction will cause the implant to rotate with respect to axis 84. Thetapered distal end 20 of implant 10 may facilitate distractionseparation or spreading apart of the adjacent vertebral bodies. Acounter lock may be provided on the installation instrument to preventstabilizer lock 88 from moving and to prevent implant stabilizer 62 fromdisengaging from implant 10 during impaction.

Referring to FIG. 14, once impacted to a desired position, the implant10 may be released from the implant stabilizer 62 by turning thestabilizer lock counterclockwise and retracting stabilizer 62 axially todisengage prongs 98 from slots 40, 46. With the implant stabilizer 62released the implant 10 is free to articulate at the end of insertiontool 28. In this regard, in this position support body 12 may rotateabout insert 14 and a central rotation axis 36 extending through thecenter of insert 14. Referring to FIGS. 15-16, once the stabilizer 62 isreleased a surgeon may impact the instrument further to advance theimplant 10 into the intervertebral space. In this regard, the outersidewall of distal end 16 of support body 12 is configured anddimensioned to contact or otherwise engage the epiphyseal ring on ananterior portion of a vertebral disc to provide force on the distal end16 causing implant 10 to rotate in-situ in the intervertebral spaceabout the axis of rotation 36. In certain methods, such rotation mayaccompany axial translation of axis 36 toward the anterior portion ofthe disc space, for example, upon impaction of installation instrument28. Referring to FIG. 16, according to one method, implant 10 may reacha desired or final installation or implantation position wherein implant10 is positioned adjacent the epiphyseal ring along the anterior portionof the disc space. Once the desired or final installation position ofimplant 10 is reached, the insertion instrument 28 may be released fromimplant 10 by unthreading the connection between insertion instrument 28and insert 14 and insertion instrument 28 may be removed from the body.In this regard, implant 10 and insert 14 are configured and dimensionedto remain implanted in the patient.

Referring to FIGS. 17-18, alternative embodiments of implants 110 and120 according to the invention are shown.

While it is apparent that the invention disclosed herein is wellcalculated to fulfill the objects stated above, it will be appreciatedthat numerous modifications and embodiments may be devised by thoseskilled in the art.

We claim:
 1. An assembly for implant installation between adjacentvertebral bodies of a patient, comprising: an implant having a supportbody and a rotatable insert therein; the support body having a proximalend portion and a distal end portion and the support body beingconfigured and dimensioned for installation between adjacent vertebralbodies; wherein the support body includes a superior surface and aninferior surface, wherein the support body defines a longitudinalopening extending between the superior surface and the inferior surface,and positioned between the proximal end and the distal portion toaccommodate the rotatable insert therein, and wherein the insert isrotatable about a central longitudinal axis within the longitudinalopening to permit the support body to rotate about the insert and thecentral longitudinal axis; and wherein the insert includes a threadedhole extending transverse to the longitudinal axis to interface with aninstallation instrument and a counter-torque slot adjacent the threadedhole and extending transversely to the threaded hole.
 2. The assembly ofclaim 1, further comprising the installation instrument removablyattached to the proximal end portion of the support body and engageablewith the rotatable insert to selectively permit rotation between theinsert and the support body, the installation instrument extending alonga longitudinal tool axis.
 3. The assembly of claim 3, further comprisingan alignment indicator disposed on a superior surface of the insert andaligned with the threaded hole.
 4. The assembly of claim 1, wherein theinsert includes a circumferential rib and the support body includes acorrespondingly shaped indentation, and the insert is captured withinthe longitudinal opening of the support body when the insert is insertedtherein.
 5. The assembly of claim 4, wherein the proximal end portionhas a rounded shape and includes one or more grooves on lateral sides ofthe implant to engage the installation instrument and wherein thegrooves are in communication with the longitudinal opening to allow apart of the installation instrument to engage the rotatable insert. 6.The assembly of claim 2, wherein the installation instrument includes acentral shaft having a threaded tip portion for threaded engagement withthe threaded hole of the rotatable insert.
 7. The assembly of claim 6,wherein the installation instrument comprises an implant stabilizerconfigured and dimensioned to engage the support body, an insertstabilizer configured and dimensioned to engage the rotatable insert,and wherein the central shaft extends through the implant and insertstabilizers.
 8. The assembly of claim 7, wherein the implant stabilizerhas a generally cylindrical body extending from a proximal end to adistal end, and wherein the distal end comprises a forked free endhaving a pair of tongs spaced apart and extending distally therefrom andthe tongs are configured and dimensioned to engage the one or moregrooves of the implant to stabilize the implant with respect to thetongs and prevent rotation of the support body with respect to thelongitudinal tool axis.
 9. The assembly of claim 8, wherein each of thesuperior surface and the inferior surface comprises a plurality ofprotrusions.
 10. A method for implant installation between adjacentvertebral bodies of a patient, comprising the steps of: assembling animplant onto an insertion tool; the implant having a support body and arotatable insert therein; the support body having a proximal end portionand a distal end portion and the support body being configured anddimensioned for installation between adjacent vertebral bodies; whereinthe support body includes a superior surface and an inferior surface,wherein the support body defines a longitudinal opening extendingtherethrough from the superior surface to the inferior surface andpositioned in between the proximal end and the distal portion toaccommodate the rotatable insert therein, wherein the insert isrotatable about a central longitudinal axis within the longitudinalopening to permit the support body to rotate about the insert and thecentral longitudinal axis; wherein the insert includes a threaded holeextending transverse to the longitudinal axis to interface with aninstallation instrument and a counter-torque slot adjacent the threadedhole and extending transversely to the threaded hole; inserting theinstallation instrument through the threaded hole such that at least oneprojection contacts the counter-torque slot; using the insertedinstallation instrument, inserting the implant into a patient betweenadjacent vertebral bodies of a patient such that the implant rotateswith respect to the longitudinal tool axis.
 11. The method of claim 10,wherein the step of inserting the implant includes: moving theinstallation instrument to a first position wherein the insert isrotationally fixed with respect to the support body and the implant isrotationally fixed with respect to the longitudinal tool axis; placingthe implant into a patient to locate the implant between adjacentvertebral bodies of a patient; advancing the implant between theadjacent vertebral bodies into an intervertebral space therebetween;moving the installation instrument to a second position wherein thesupport body is rotatable with respect to the insert; advancing theimplant further into the intervertebral space such that the implantrotates with respect to the longitudinal tool axis.
 12. The method ofclaim 11, wherein the distal end of the implant is tapered andconfigured to separate the adjacent vertebral bodies when theinstallation instrument is in a first position and the implant isadvanced into the intervertebral space.
 13. The method of claim 11,wherein a lock is provided on the installation instrument to prevent theinstrument from disengaging from the implant during impaction.
 14. Themethod of claim 11, wherein the implant and insert remain implanted inthe patient.
 15. The method of claim 11, wherein the superior surfaceand the inferior surface comprise protrusions.
 16. The assembly of claim1, further comprising a second longitudinal opening surrounded at leastin part by one or more protrusions.
 17. The assembly of claim 1, whereinthe support body further includes a groove that extends adjacent theproximal end portion and extends along an interior curved wall of thesupport body.
 18. The assembly of claim 1, wherein the insert includes acircumferential rib that mates to a corresponding indentation shaped onthe support body.
 19. The assembly of claim 1, wherein the installationinstrument comprises an implant stabilizer and an insert stabilizer.